Not sure if this is a bug report or a feature request. The Musician field allows you to add a default instrument, but that relationship doesn’t seem to hold for folders. For example, if I create folder view Instrument/Musician, I’d expect to see instruments and sub folders showing musicians associated with that instrument, and the albums on which they appear. Likewise the inverse, for Musician/Instrument I’d expect to see subfolders for the instrument associated with that musician, but it doesn’t seem to work that way. In the Instrument/Musician view, all I get is a list of albums on which the instrument appears, but no sub folders for the musicians with that instrument. So I can see, for example, a list of all albums with flute, but not albums on which Eric Dolphy plays flute.
It would be awesome if these very useful fields were linked in a way to allow going down a level to see all artists who play bass, followed by the albums on which they play.